# Endocrine Disruptor

Screening Program ( 

# EDSP) Weight of Evidence ( WoE ) Concluding Remarks
Thomas M. Steeger, Ph.D. Environmental Fate and Effects Division Office of Pesticide Programs Office of Chemical Safety and Pollution Prevention U.S. Environmental Protection AgencyStructure Activity Relationships In vitro Studies In vivo Studies

2 Population Studies/Models 

###  How responses are integrated from diverse studies
 How the strength of evidence is determined by evaluating varying degrees of complementarity and redundancy in responses
 How OSRI data are used to further characterize Tier 1 findings 

## Application of Adverse Outcome Pathway Concept Demonstrates:

# Case Study A — Androgen Antagonism

Intact HPG 

## Tier 1 Assays

Rat Pubertal & OSRI - anti - androgenic responses were not observed at a higher level of biological organization presumably due to compensatory

mechanisms. 3

# Chemical A

 Androgen Antagonism

 An example of a compound that has potential to initiate a pathway but interaction is not robustly expressed in organisms with an intact HPG

 An example of FSTRA decision logic
—
• Only 2 endpoints impacted that lack specificity (GSI and gonadal histology) in absence of overt toxicity

• Responses coincident with overt toxicity at higher doses may be nonendocrine and reflective of generalized toxicity

 Absence of robust complementarity and redundancy in responses do not support potential interactions with estrogen signaling pathway

 Equivocal in vitro ; negative mammalian; FSTRA lacks dose response and complementarity in responses

 Lack of robust complementarity and redundancy to support HPT axis interaction

 AMA negative; marginal responses in T4
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## Case Study S — E and A Pathway Interactions

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## Tier 1 Assays

OSRI - no effects found 

### Estrogen Pathway

Androgen Pathway

# Chemical S

 

## Limited complementarity and redundancy in 

## responses support potential interactions with estrogen signaling pathway

 

## Lack of robust complementarity and redundancy 

## to support HPT axis interaction

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# Case Study J — Androgen Antagonism



# (altered steroidogenesis)

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## Tier 1 Assays

Weak AR binding and Negative Hershberger does not support AR binding as the MIE OSRI - effects consistent with Tier 1 assays

# Chemical J

 Androgen Antagonism

 An example of a compound that has potential to initiate a pathway and robustly express responses at higher levels of biological organization in organisms with an intact HPG

 Robust complementarity and redundancy

• FSTRA and male pubertal responses diagnostic of A interaction

 Absence of robust complementarity and redundancy in responses do not support potential interactions with estrogen binding signaling pathway

 ER binding and ERTA in vitro negative
 Female mammalian in vivo negative; however open literature discusses observed differences between rats and fish

 Lack of robust complementarity and redundancy to support HPT axis interaction

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# Case Study N — Androgen Antagonism

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## Tier 1 Assays

* No effect on receptor mediated signaling OSRI - no relevant effects

# Chemical N

 

### Androgen Antagonism

 MIE is unclear but has potential to initiate a pathway with responses expressed in organisms with an intact HPG near limit doses/concentrations

• limited complementarity and redundancy within in vivo assays


###  

### Absence of robust complementarity and redundancy in 

### responses do not support potential interactions with estrogen binding signaling pathway

 FSTRA lacks dose response and complementarity in responses


###  

### Negative responses (AMA: Rat) do not support HPT axis interaction

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# Case Study X — Estrogen Antagonism

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## Tier 1 Assays

# Chemical X

 

### Androgen Antagonism

 AR binding and ARTA are likely MIE but it is unclear if Chemical X has potential to initiate a pathway in organisms. Discrimination between estrogen agonist and androgen antagonist in organisms with an intact HPG is difficult.

• Negative Hershberger assay, limited androgen - specific effect in vivo assays


###  

### Estrogen Agonism

 A high degree of complementarity and redundancy in estrogenic responses strongly support potential interactions with estrogen signaling pathway


###  

### HPT Interaction

 Alterations in T4 and TSH in mammals suggest possible HPT axis interaction, however, no AMA analogue

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# Adverse Outcome Pathways (AOPs) and the Weight of Evidence ( WoE )

 

## Competing AOPs
 Endocrine versus non - endocrine pathways or mechanisms of pesticidal mode of action that lead to overt toxicity
 Integrate understanding of overt toxicity

• Chemical A
— cholinergic intoxication due to cholinesterase inhibition

• Chemical S
— uncoupling of mitochondrial oxidative phosphorylation and depletion of ATP; irritation that compromises the integrity of the gastro - intestinal tract

• Chemical N
— nonpolar narcosis

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# In Summary

 

## Approach articulated in 2011 EDSP WoE guidance
 Promotes systematic use of data
 Focuses on what is known about underlying biology as described in the AOP as an aid in the WoE process  Understanding degree of complementarity and redundancy in observed responses, as well as, the conditions under which responses occur provides 

### basis for judging biological plausibility

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# In Summary The Agency is seeking comments from the SAP on the implementation of the basic interpretive process of the WoE guidance as illustrated with five case studies

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# Next Steps

 

## Conduct a systematic literature review for public 

## literature on E, A and T

 

## Integrate different lines of scientific evidence 

## using the Adverse Outcome Pathway

 

## Finalize weight of evidence assessments for all List 1 chemicals, considering the recommendations made by SAP

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